There is a great demand for experienced J2EE
professionals now in the market and students and programmers from other
languages want to know whether J2EE is Java atall or something else. This
tutorial is a conceptual presentation of what & why of J2EE.
(It is better for aspiring Java professionals to be forewarned that
the Industry expects sound knowledge of EJB, JAX and Struts ..as well as
hands on experience in Application servers like WebLogic /WebSphere as
a MINIMUM! .It is also important to remember that jdk1.4 is
the current version with a lot of new features and jdk1.5 is
expected shortly. Moreover, Security in computing is assuming great
importance and the candidate should have sound knowledge about java
security.)

J2EE is not the Java , that
comprises of topics like Applets, Console- mode programs, Standalone GUI,
Multithreading, Graphics,Exception-handling, String processing, IO
Streams, Java Beans in BDK, Swing etc.( topics covered in great detail by
books on Core Java , such as 'Java2 -complete reference' by Schildt.,with
not a word anywhere on that staple of Computing world of any type (ie)
DataBase access!)

The title of the book was appropriate some
7 years back! That is why we are puzzled and dismayed that the Java that
we studied so 'completely' is so basic and
so incomplete!..To be fair, even with the arrival of jdk1.1,some authors
like Bill McCarty ('Java ..Distributed Objects') and Jaworsky ('Java2
Unleashed') had a better perspective about the Enterprise potential
& orientation of Java and wrote accordingly. However, they are being
mentioned only now in curricular circles. after what they wrote so
well has sadly become , partly outpaced..This is not to
say that Core Java is useless. As the name suggests, it is the core and
absolutely essential . But, Java has always been a language for the Web
and Enterprise. Without that essential paradigm shift from desktop/LAN to
the sprawling WEB & huge enterprise data, it is very difficult
to appreciate the modern trends and why there is so much clamour for J2EE
(despite the supposed challenge from DotNet). The only topics
that could bridge the Core and Enterprise Java are Sockets
& Beans.

(Among
web-professionals, there is a fancy for JavaScript, which is
mostly used in Client-side webpages ..It's only use should be
'client-side' validation and no gymnastics. JavaScript is in no way
connected with Java . It is unfortunate that this 'script' originally
known as 'Live Script' from Netscape , got mixed up with Java . When any
one talks about Java Script in the same breath as Java, he is missing
Enterprise Java, the true essence of Java language.

For aspiring J2EE professionals, ' the less
javascript, the better' should be the motto.). We will begin
with what Javabean is and also see how beans can be used in
Socket programming. Then we will bring out the difference between
invoking the method on a bean in a remote server by passing
arguments & the Distributed Object paradigm. We will also explain why
Distributed Object Technology is not just Client-server or
Web-server technology and why it is superior. Finally, we will see why
Distributed Object Technologies like EJB ,CORBA & DCOM were
found to be wanting in true inter-operability and how the problem is being
sought to be tackled by the latest approach (ie) XMLWEBSERVICE.

This, however, is pretty
long journey and this 'short' tutorial cannot cover all the
details. The readers are equested to refer to the books mentioned
towards the end to get more details.

J2EE ( Java 2 -Enterprise
Edition) is a basket of 12 inter-related technologies , which
can be grouped as follows for convenience.:

J2EE is essentially about
Distributed Objects Technology, which is defined as
invoking a method on an object residing in a remote machine as if it
were local to the invoking program. The Distributed Object may be
based on RMI or IDL or RMI-IIOP or EJB.

The invoking program can be a standalone
mode java program. But , if this were so, it presents two problems.
The first problem is that it requires JDK to have been installed in
each end-user's machine.This is not a correct assumption because, the only
thing that we can be sure of is that the end-user has a browser.

Secondly, even with JDK installed in the end-user
machine, the java program has to be distributed to each client
personally.. This is hardly a practical proposition, if we want our
program to be useful to lakhs of end-users out there.

Applets, are a possible solution. An applet is a java class file
embedded in HTML document, downloaded from the web server and executed
in the end-user's browser.( The browser should be
java-enabled). With built-in sandbox security, Applets made
program distribution very easy and elegant.

However, Applets also had two problems. First, standard browsers
like InternetExplorer(Microsoft) and NetscapeNavigator (NetscapeCorporation)
did not implement JDK fully. This required a java-plug in from
Sun.This was clumsy. Secondly, java applets, except in very simple cases,
downloaded the classes from the server and though this is a
remarkably powerful feature, it also meant that the process was a heavy
one and entailed delay in downloading.

For
these reasons, Applets also ceased to be the recommended method.
That is why Sun developed the Servlets technology. Servlets are
java class files , execeuted in server and the resulting html
sent to the end-user's browser. Now, at one stroke , it solved many
problems.

1) We no longer had to instal JDK in end-user's machine.

2) We need not have a java-enabled browser at the user's end.

3) As the result was sent as html only to the browser, it is
lightweight & very fast.

But, this creates a different
problem! A WebServer is just for delivering documents as requested
by the user. It need not have any scripting features. Various Webservers
have built in facilities for executing CGI and CGI like programs.
For instance, Personal WebServer has built in feature for executing ASP
which uses VBScript. Apache server provides PERL & PHP. Similarly ,
JavaWebServer provides Servlet engine and JSP engine. Realising
that Apache is the leading WebServer in Internet world, Sun
collaborated with Apache Foundation and created the Tomcat engine.
We must remember that not any web server can execute a servlet.. So,
the correct method of invoking the function on a remote object in remote
server is through a servlet. The modern practice is to have a
thin client.(ie) the end user has just a browser like InternetExplorer
or Netscape Navigator. He downloads an HTML form and invokes a servlet or
JSP through the form.

If Distributed
Objects are not involved, the servlet/jsp does the processing
in web server itself and sends the result to the browser. For
Distributed Computing , however, the servlet program in the web-server is
the client-side for the Distributed Object computing.It invokes the
method of the remote object in the Remote Server. ( it may be
RMI/IDL/RMI-IIOP/EJB).The result is sent to the end-user's browser. . All
this may be very dense fog right now but will
clearup as we progress.

With these introductory remarks, let us now take
up the technologies one by one.

Group1========

Servlets & JSP are Web-server technologies.(
Distributed Objects Technologies are the more advanced
stage...covered in second group) In most of the cases the requirement is
that a database is to be accessed either for queries or for
modifications . So we use a jdbc program in the webserver and
access the database & send the result to the user's browser.

Apart from this , it is also
very useful to be able to send email through the server.
These two opeartions (ie) database operation & mailing are
essential applications in webserver. That is why JDBC & JavaMail have
found a prominent place in the first group of J2EE technologies.

JSP , is a technology which tries to
separate the code from the presentation.( However, new developments
like JSTL (Java Standard Template Library) & Struts have
appeared which insist on much higher degree of separation between code
& presentation.JSP-2 is awaited and it aims at total
elimination of java code anywhere in the JSP page!..something that ASP.NET
has already achieved!).

mohammed shahnoorbaba
January 23, 2012
Requesting for continuation for above topic
when i press next button iam getting the same page

Inspire
February 2, 2012
j2ee
NICE!!!!

jazzy java
April 10, 2012
Next page?
The Next link doesn't work. Please provide the link to the next page showing group 2 etc. Thank you.

pawan mishra
August 7, 2012
comment
its amazing.

gayathri
October 14, 2012
j2ee
i want to download this material

arvind sharma
November 18, 2012
j2ee
i want to known ki which language use in cloud computing mostly please tell me use of j2ee in year 2013 mostly because i am afresher student is in this java j2ee feture is brieght or not give me ans